1. Field of the Invention
This invention relates to ink jet recorders and in particular to an ink jet printer in which individual drops of an ink jet are projected onto a record medium to record characters or other information in accordance with dot matrix pattern.
2. Description of the Prior Art
Ink jet recorders for printing dot matrix characters, such as alphanumerics or the like, on a print medium are well-known. Basically, such recorders operate by projecting a continuous stream of ink drops of substantially uniform size and spacing along an initial trajectory toward a print medium. The drop generation rate is substantially uniform and is dependent on the number of coordinate intercepts of the matrix field pattern and the desired speed at which characters are to be recorded on the print medium. Dot matrix characters are formed by the process of selectively intercepting certain, i.e., unwanted, drops of the stream and controllably dispersing the remaining, i.e., print, drops onto the desired coordinate matrix positions corresponding with the desired character shapes. The dispersion of the print drops to form the desired character basically depends on deflection of the drops in a first direction orthogonal to the stream trajectory concurrent with relative motion of the ink jet stream and the print medium in a second direction mutually orthogonal to the first direction and the stream trajectory. Dot matrix characters formed in accordance with this technique basically take unconventional shapes which affect print quality. This is due largely to the fact that the line segments formed by the drops are substantially straight and the available angles for printing the characters is limited. For example, the capital letter B and the numeral 8 are difficult to distinguish when the characters are formed from straight line segments of a square matrix.
Various methods have been devised to improve the print quality of dot matrix characters formed from a square matrix. One approach has been to omit dots at corner positions to give the visual suggestion of an arcuate character segment. This approach, however, destroys line continuity and reduces print quality. Another approach has been to give one or more characters unconventional shapes to distinguish it from a similar-shaped character. This, however, provides difficulty to persons not familiar with the unconventional shape. Another approach has been to deflect the stream in accordance with coordinate analog signals which essentially produce cursive line traces of characters. While this approach permits arcuate line segments to be formed, the electronics for obtaining the analog tracing is very complex and difficult to control. Another approach is to make the dots smaller and increase the matrix density. This approach, however, reduces the possible print throughput and increases the complexity for controlling the individual drops. Also, smaller drops are more susceptible to aerodynamic disturbances.
A further problem in dot matrix character printing is that solid lines composed of dots have a cusp-like edge more or less visible depending on drop size and the amount of overlap. The depth of the cusp is dependent on drop size and the degree of overlap. Also, whatever drop size is used the depth of the cusp is greater for line segments on a diagonal than for lines on the horizontal and vertical.